This invention relates to a transmission network such as a synchronous transmission network and, more particularly, to an apparatus for administrating the transmission network.
Recently, a transmission network of the type is actively utilized by many operating companies. The transmission network includes a plurality of communication routes parallel to one another. Each of the communication routes has at least two crossconnect systems. Any one of the crossconnect systems may be used in common in two or more ones of the communication routes. Communication is carried out through a path, namely, a particular one of the communication routes.
It is assumed that a failure occurs in the particular route. Such occurrence of the failure results in serious damage to the operating company. It is therefore required to carry out a switching operation which is for switching the path from the particular route into another one of the communication routes as immediately as possible after occurrence of the failure.
In Japanese Patent Prepublication (Kokai or Publication of Unexamined Patent Application) Nos. 58542/1991 and 117140/1991 for inventions by Yasuyo Nisimura, a specific logical algorithm is disclosed in order to carry out the switching operation. When the failure occurs at a particular point in the particular route, an alarm indication signal is generated at the particular point in the manner known in the art. In response to the alarm indication signal, execution of the specific logical algorithm is initiated in each crossconnect system to make a combination of the crossconnect systems carry out the switching operation.
Generally, an add drop multiplexer and a line terminating equipment are connected between the crossconnect systems. Accordingly, it will be assumed that the add drop multiplexer or the line terminating equipment is interposed between the particular point and each of the crossconnect systems. A line alarm indication signal is known as the alarm indication signal. The line alarm indication signal is terminated at each of the add drop multiplexer and the line terminating equipment and does not reach each crossconnect system. As a result, execution of the above-mentioned specific logical algorithm is not started in each crossconnect system.
A path alarm indication signal is also known as the alarm indication signal. The path alarm indication signal arrives at each crossconnect system without being terminated at each of the add drop multiplexer and the line terminating equipment. By the use of the path alarm indication signal, it is therefore possible to start execution of the specific logical algorithm in each crossconnect system even if the add drop multiplexer or the line terminating equipment is interposed between the particular pint and each of the crossconnect systems.
It is also assumed that an additional crossconnect system is interposed between the first-mentioned crossconnect systems. In this event, execution of the specific logical algorithm is started also in the additional crossconnect system in response to the path alarm indication signal. This results in an disadvantage in the switching operation.